Method of sending and receiving radio frequency impulses



3 H2, 1940. P. KOTOWSKI El AL 2,192,975

METHOD OF SENDING AND RECEIVING RADIO FREQUENCY IMPULSES Filed Jan. 2'7, 1938 2 Sheets-Sheet l 4H; JHHHHIHHHH H H H H Paul Katowshl, (Sigmund efibnnenfeld, 5 @ottfried V095 dt torneg March 12, P, KOTOWSK] ET AL METHOD OF SENDING AND RECEIVING RADIO FREQUENCY IMPULSES Filed Jan. 27, 1938 2 Sheets-Sheet 2 7/69/1/5fl7/77E/8 M0708 5/2550 gawk/vale Patented Mar. 12, 1940 Z,12,9 75

UNITED STATES PATENT OFFICE METHOD OF SENDING AND RECEIVING RADIO FREQUENCY IMIPULSES Paul Kotowski, Berlin-Tempelhof, Sigmund Sonnenfeld, Berlin-Schoneberg, and Gottfried Vogt, Berlin-Tempelhof, Germany, assignors to Telefunken Gesellschaft fiir Drahtlose Telegraphic in. b. H., Berlin, Germany, a. corporation of Germany Application January 27, 1938, Serial No. 187,288 In Germany February 4, 1937 6 Claims. (Cl. 250-11) This invention relates to the transmission and for direction finding. It is only this ground wave reception of impulses for use in direction finding that results in true bearings. devices, and the like. More particularly, this However, in procticing any of these methods invention relates to a system for increasing the serious difficulties frequently arise on account of signal-noise ratio in a direction finder of the the fact that at greater distances it is often im- 5 impulse type by receiving-impulses of very short possible to identify the impulse from among the duration on a receiver having a wide band-width various stray signals and static that are picked characteristic to obtain maximum accuracy durup by the receiver. In fact, for clear discriminaing periods which are free from static disturbtion or separation, the signal impulse amplitude 0 ances and increasing the signal-noise ratio in must surpass the amplitude of the stray signals the presence of static by decreasing the bandat least by a factor of two. width characteristic of the receiver, thus elim- It is known that a rectangular impulse can be inating the short impulses, and providing imconsidered as being composed of a large number pulses of longer duration for use with the reduced of different frequencies. Consequently, in order 5 band-width to provide an indication. to repro a angular impulse without dis- This invention will be better understood from tortion a wide band receiver is necessary. It can the following description when considered in conbe shown that the band width which is required nection with the accompanying drawings, in to reproduce a rectangular impulse is inversely which: proportional to the length or duration of the im- 0 Figure 1 shows t nature of t signal ent pulse. It is also known that the amount of static out by the transmitter of an impulse direction and noise which is picked up y a eceiver is definding system; pendent upon the receiver band-width charac- Figurg 2 shows th nature of th impulses teristic. The narrower the band-Width, the less cording t thi i ti the noise which will be received.

5 Figure 3 shows an alternate form of impulse In cases of this kind where static is bad a arrangement; longer impulse would be more suited since it Figure 4 shows another arrangement of the would make it feasible at the receiving end to impulses; utilize. a receiver having a narrow frequency Figure 5 shows th nature of th impulse of band; and, as a result, the ratio of the stray noise 0 Fig 4 after t has been i d; amplitude to the impulse amplitude could be Figure 6 is a simple transmitter adapted to diminished. The extent to which the band-width carry out this invention; and can be decreased is limited by the relation Figure '7 is a receiver for use in connection 1 with this invention.

5 In order to obtain direction-finding under conditions free from night effects, recourse has been where J is the band-width of the receiver and T1 had to impulse direction-finding. A transmitter is the length of the impulses in seconds. Further or beacon station sends out periodically impulses que cyompression will then aiiect the of a duration T (Fig. l) The time T is substan- S gna a d the St ay amplitude or height in like -0 tially less than the time required for the impulse DrOpOrtiOn d is therefore W out any practical 40 to reach the receiver, and the interval between pu p On the other hand, a narrow impulse impulses is greater than the transit time, as is (T2) affords greater accuracy in reading; and well known. At the receiving end, not only the When app to impulse -fi d g it algrcund wave but also the space or sky wave with 10WS mere accurate Position finding.

5 its various echoes resulting from such impulses According to this invention, therefore, alterare picked up. However, inasmuch as the time te y a Wide a d. a ow impulse (Fig. 2) or of transit of the sky or space wave is greater than groups of broad and of ow impulses are sent that of the ground wave, the result is that the Out W en interference is bad the r signals which travel to the receiver over difi'erent eeivel bend-Width is uced, that is, its selec- 0 paths will reach the receiver one after the other tivity is increased to eliminate or reduce the (in time sequence). It is known that by the aid interference A15 the Same me this prevents the of suitable indicator means, such as a Braun or undistorted reception of y 511011? pulses, T2, cathode-ray tube, ground and space waves may but allOWS the reception of the longer impulses be separated from each other, with the result T1. While the accuracy of the direction indicator .5 that only the ground or direct wave is utilized is somewhat reduced, reception is accomplished where it would otherwise have been impossible. When conditions are good, the receiver bandwidth is increased and the short impulses utilized to provide an accurate determination of direction. Another scheme as shown in Fig. 4 would be to transmit groups of narrow and closely adjacent impulses which, upon compression of the incoming frequency band would be caused to coalesce into what is effectively single impulse (Fig. 5) having an impulse period T4. The impulse duration of the wide and the narrow impulses as shown in Fig. 3 amount to T1 and T2, respectively. Of course, the impulse width could also be steadily varied with time.

Compression or contraction of the frequency band at the receiving end is accomplished by a variation of the transmission characteristic of the receiver. As known in the art, this may be done for radio frequency either by altering the damping of the circuits or by variation of the coupling. Finally, also the audio frequency transmission characteristic could be regulated by a variable low-pass filter.

Fig. 6 illustrates a transmitter which will transmit alternate short and long pulses of the type illustrated in Fig. A transmitter T is coupled to an antenna A, the ground connection to which is made through a commutator C. The commutator has alternate short and long contacting members which are insulated by a suitable in sulating material. Upon rotation the commutator intermittently completes the antenna circuit to ground, producing short impulses whose relative duration and spacing are determined by the construction of the commutator.

A motor M is used to drive the commutator at a suitable rate of speed so that the duration of each impulse is or" the order of .00015 second. The motor is driven at a constant speed by a speed governor F. The illustrated transmitter is a modification of a transmitter shown in U. 3. Patent No. 2,031,677, filed February 3, 1933, and issued February 18, 1936 to S. B. Smith, et al. The modification comprises the arrangement of the commutator to produce the desired short and long impulses. It will be understood how the commutator may be arranged to produce impulses of the types illustrated in rigs. 2 to 5.

Fig. 7 is a directional receiver arrangement of the general type disclosed by Chireix in U. S. Patent No. 2,059,315, filed July 17, 1935, and issued November 3, 1936. The receiver R however, is a variable band-width receiver, for example of the type disclosed in a patent of Carlson, No. 2,133,808, filed September 27, 1933, and issued October 18, 1938. The scanning voltage generator S is synchronized with the speed governor F in any well known manner.

We claim as our invention:

1. in a direction finding system which comprises an impulse transmitter and a directive variable band-width receiver, the method of op eration which consists of transmitting impulses of dilierent effective duration, the duration of said impulses being less than the transit time from said transmitter to said receiver, receiving said impulses, and adjusting the band-width of said receiver to receive effectively short impulses in the absence of static and other interference and adjusting the band-width of said receiver to receive efiectively long impulses in the presence of static and other interference.

2. In a direction finding system which utilizes an impulse transmitter and a directive variable band-width receiver, the method of maintaining an indication in the presence of interfering noises and static which includes the steps of generating and transmitting impulses of non-uniform time duration, receiving said impulses, the time duration of said impulses being less than the transit time of an impulse, and utilizing the shorter of said non-uniform impulses to indicate direction when interference and static are not excessive, and utilizing the longer of said impulses to indicate direction when receiving conditions do not permit the use of said shorter impulses.

3. In a direction finding system which comprises an impulse transmitter, and a directive variable band-width receiver, the method of maintaining an indication in the presence of interference and static which includes the steps of generating and transmitting impulses of nonuniform time duration, said time duration being appreciably less than the transit time between said transmitter said receiver, adjusting the band-width of said receiver to receive the shortest of said impulses in the absence of interfering noises and static, and adjusting the band-width of said receiver to pass only said impulses of long duration in the presence of interfering noises and static, thus also reducing said noises and static.

i. In a direction finder which comprises an impulse transmitter and a directive variable bandwidth receiver, the method of operation which includes the steps of transmitting alternate short and long impulses, said long impulses being of less duration than the transit time required for an impulse to pass from said transmitter to said receiver, and the interval between impulses being longer than said transit time, receiving said pulses, increasing the band-width response of said receiver to pass said long and said short impulses, and utilizing said short impulses to accurately determine a direction, and, when necessary,

decreasing the band-width response of said receiver to reduce interference and static, thus reducing or eliminating said short impulses, and utilizing said long impulses to give a less accurate but static-free indication of direction.

5. A method as set forth in claim 1 in which said impulses of different efiective duration constitute groups of short closely adjacent impulses. 6. A method as set forth in claim 1 in which said impulses of different effective duration constitute alternate groups of long and short impulses.

PAUL KOTOWSKI. SIGMUND SONNENFELD. GOTTFRIED VOGT. 

